In the operation of a continuous ink jet printer, a continuous jet of ink drops is formed. Usually, the drops are deflected in flight so that only some drops are used for printing. Drops of ink that are not required for printing are caught by a gutter and are returned to an ink tank within the main body of the printer. In an electrostatic deflection ink jet printer, this deflection is performed by trapping electric charges on some or all of the drops of ink, and using an electrostatic field to deflect the charged drops so that the printer prints the desired printed pattern. The ink includes a solvent which is normally highly volatile so that the drops of ink dry quickly after printing. The solvent also tends to evaporate from the ink that is caught in the gutter and returned to the ink tank, so that the ink used by the printer loses solvent over time. In order to maintain the correct ink viscosity, additional solvent is added from time to time. Additionally, the ink is slowly used up as the printer prints and therefore the ink in the ink tank needs to be replenished.
In order to stop and start the ink jet, and perform other operations such as adding ink and solvent, sucking air into the ink gun used to form the ink jet, and to apply or withdraw suction from the gutter, various valves are required within the ink system. The ink system will also normally include other electrical components, such as an ink pump for pressurising the ink and a pressure sensor for sensing the ink pressure. The suction for the gutter, and for applying suction to the interior of the ink gun if necessary, is often provided by a Venturi device which generates suction from the flow of ink through it. The ink is pumped through the Venturi by the ink pump, and the ink that flows through the Venturi is returned to the ink tank.
In order to add solvent to the ink in the ink tank from time to time, it is possible to provide a supply of solvent in a solvent tank and to use the Venturi device to suck a small amount of solvent from the solvent tank into the ink that flows through the Venturi and is returned to the ink tank. When the solvent tank gets low it can be topped up by the operator. In a similar way, the ink in the ink tank can be topped up by the operator as necessary. However, owing to the possibility of spills it is preferred to fit a removable solvent container such as a bottle or cartridge into the machine, and similarly to fit a removable ink container, such as a bottle or cartridge into the machine, and arrange for the printer to withdraw solvent and ink from the containers as necessary. The containers are replaced by the operator when they are empty. The likelihood of substantial spills of ink or solvent is reduced because the operator should only be handling the removable containers either when they are full and sealed or when they are empty. The ink and solvent containers can be arranged to supply ink and solvent reservoirs, from which the printer sucks ink and solvent as required, or the ink and solvent can be sucked directly from the containers.
It is known to hold the ink and solvent containers in the printer with a substantially liquid-tight seal, so as to minimise the possibility of spillage from the containers especially if the printer is tilted or jolted as it is carried from one place to another. However, systems in which the ink and solvent containers are sealed into the ink system of the printer typically have the effect that ink and solvent must be sucked out of the containers without the possibility of air entering the containers to replace the volume of liquid that is removed. Consequently, the containers have to deform so that their internal volumes reduce as liquid is removed. Therefore the suction applied to remove ink and solvent from the containers must be sufficient to overcome the containers' resistance to deformation. In practice, the suction provided by a Venturi is usually adequate for this purpose and it is known to suck solvent from a sealed reservoir and/or container using a Venturi. However, the Venturi only generates suction when ink is flowing through it. This means that the Venturi cannot be used to suck liquid from a container when the printer is initially being commissioned or at any other time when there is little or no ink in the ink tank, because the ink pump cannot pump ink through the Venturi to generate suction under these circumstances. Therefore, it is known to suck ink out of the ink container using a diaphragm pump, which has the advantage that it can develop adequate suction to remove ink from the ink container without needing already to contain ink in order to operate.